A battery unit is, for example, described in JP-A-2003-346759. The described battery unit includes a battery module assembly as a battery, which is an important part, and a blower for cooling the battery module assembly. The battery module assembly is housed in a battery cover. The blower has a blower casing. The blower casing is connected to the battery cover at a position above the battery module assembly, and a passage of the air is defined therein.
Such a battery unit is, for example, mounted in hybrid vehicles. Thus, silence is required in an eco-running mode in which an engine is stopped. Also, in a case where the battery unit is arranged on a rear side of a luggage room of the hybrid vehicle, it is generally required to be compact.
In the described battery unit, the battery module assembly is inclined downward toward the blower relative to a flow direction of the air blown from the blower. Because a predetermined passage is defined between an upper inner surface of the battery cover and an upper surface of the battery module assembly, resistance to flow of the air is reduced, and hence noise is reduced. On the other hand, a size of the battery unit including the battery cover and the blower casing increases due to the passage being provided by the arrangement of the battery module assembly.